Deformation history of Archean metasedimentary rocks of the Beartooth mountains in the vicinity of the Mineral Hill mine, Jardine, Montana
- Univ. of Minnesota, Duluth (United States)
Archean metasedimentary rocks of the South Snowy Block of the Beartooth Mountains, in the vicinity of Jardine, Montana, consist predominantly of schistose rocks with rare iron formation. These rocks are intruded by Precambrian granitic stocks and minor mafic dikes and sills. Evidence for three phases of folding and late-stage kinking is found within the metasedimentary rocks, whereas rocks of the Crevice Mountain stock (2,700 Ma) are unaffected by any of these events. The first folding event involved the development of isoclinal, recumbent folds of varying scale. F[sub 1] fold hinges are rare, most commonly observed underground in Mineral Hill. An S[sub 1] schistosity has developed axial planar to these folds. This schistosity, which is subparallel to bedding, is very well developed and ubiquitous in the metasedimentary rocks of the Jardine region. Two later phases of folding are also recognized. F[sub 2] folds are nearly upright with gently to moderately plunging fold hinges. Temperature and pressure conditions during deformation, as revealed by calculations from microprobe analyses, suggest that the peak of metamorphism occurred at a temperature of about 560 C and a pressure of 2.9 kb. Thin section observations indicate that the metamorphic peak accompanied the formation of S[sub 1] schistosity. Structural, metamorphic, and geochemical data are consistent with the hypothesis that the metasedimentary rock of the Jardine region are allochthonous and constitute one of a number of tectonostratigrphic terranes in the western Beartooth Mountains that were juxtaposed tectonically against the western margin of an Archean continent during a Late Archean collisional event.
- OSTI ID:
- 6937663
- Journal Information:
- Journal of Geology; (United States), Vol. 100:5; ISSN 0022-1376
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
GEOLOGIC FORMATIONS
TECTONICS
MONTANA
SCHISTS
GEOTHERMOMETRY
PETROGENESIS
ANTICLINES
DEFORMATION
GEOCHEMISTRY
GEOLOGIC HISTORY
PETROCHEMISTRY
PRECAMBRIAN ERA
CHEMISTRY
DEVELOPED COUNTRIES
FEDERAL REGION VIII
GEOLOGIC AGES
GEOLOGIC STRUCTURES
METAMORPHIC ROCKS
NORTH AMERICA
ROCKS
USA
580000* - Geosciences